1. Field of the Invention
The present invention relates to a fabrication method of a liquid crystal display (LCD) device, and more particularly, to a fabrication method of a color filter panel using a reduced number of mask processes.
2. Description of the Related Art
Generally, an LCD device is for displaying an image by using a liquid crystal driven by an applied signal, and is largely composed of an upper plate, a lower plate, and a liquid crystal between the upper and lower plates.
The upper plate is generally known as a color filter panel or substrate for displaying an image in colors. The lower plate is generally known as a thin film transistor (TFT) array panel or substrate having unit pixels arranged in a matrix form and provided with TFTs at each unit pixel as a switching device.
The structure of an LCD panel constituted with an upper plate 200 and a lower plate 100 will be explained with reference to FIG. 1.
As shown in FIG. 1, in the lower plate (TFT array panel) 100, a plurality of gate lines 101 arranged in parallel cross perpendicularly a plurality of data lines 102 arranged in parallel on a lower substrate 105. Intersection regions between the gate lines 101 and the data lines 102 are defined as unit pixel regions, where the unit pixel regions are arranged in a matrix form on the lower substrate 105. At each intersection region between the gate lines 101 and the data lines 102, a switching device 103 for driving the corresponding unit pixel is formed. As the switching device, a TFT is generally used. The TFT includes a gate electrode, a source electrode, a drain electrode, and a channel layer. The gate electrode and the source/drain electrodes are respectively connected to the corresponding gate line 101 and the corresponding data line 102.
For each unit pixel region, a pixel electrode 104 for applying an electric field to a liquid crystal 110 is formed at the lower substrate 105. An alignment layer (not shown) for the initial alignment of the liquid crystal 110 is formed on the pixel electrodes 104 over the entire surface of the lower substrate 105. As the alignment layer, a polyimide-based organic layer is used. The initial alignment of the liquid crystal 110 is performed by depositing the alignment layer and performing a rubbing process for rubbing the alignment layer with cotton.
A spacer (not shown in FIG. 1) for evenly maintaining a gap between the lower plate 100 and the upper plate 200 is arranged on the alignment layer. A sealant for bonding the upper plate 200 and the lower plate 100 and preventing the liquid crystal 110 from being leaked is formed at the periphery of the pixel region of the lower plate 100.
The structure of the upper plate 200 opposing the lower plate 100 and displaying information in colors will be explained.
In the upper plate 200, a black matrix 202 for shielding unnecessary light among the light irradiated from the lower plate 100 is provided in a matrix form. On the black matrix 202, a color filter layer 203 for displaying an image in colors is provided. The color filter layer 203 is composed of R, G, and B sub color filter layers each corresponding to one of the unit pixel regions.
An overcoat layer 204 for compensating any step in the color filter layer 203 may be provided on the color filter layer 203. A common electrode 205 for applying an electric field to the liquid crystal 110 with the pixel electrodes 104 formed at the lower plate 100 is provided on the overcoat layer 204. On the common electrode 205, an alignment layer (not shown) for the initial alignment of the liquid crystal 110 is provided. A spacer (not shown) for maintaining a cell gap between the upper plate 200 and the lower plate 100 may be provided on this alignment layer. As known, a spacer can be provided either at the upper plate 200 or at the lower plate 100.
FIG. 2 shows the structure of the upper plate (color filer panel) 200 of the LCD device of FIG. 1 in more detail.
Referring to FIG. 2, on a color filter substrate 201 of a transparent material, the black matrix 202 is provided. The black matrix 202 is formed of a metal thin film or a resin, and is arranged in a matrix form so as to correspond to the gate lines 101 and data lines 102 formed on the lower substrate 105. A color resin as the color filter layer 203 for displaying an image in colors is formed in a pixel region defined by the black matrix 202. The color resin is composed of R, G, and B colors, and is arranged to correspond to each unit pixel. On the color filter layer 203, the transparent overcoat layer 204 for compensating steps in the color filter layer 203 and protecting the color filter layer 203 is provided. On the overcoat layer 204, the common electrode 205 composed of a transparent material for applying an electric field to the liquid crystal 110 is provided. On the common electrode 205, a spacer 206 for maintaining a cell gap of the LCD device is formed. On the spacer 206, an alignment layer 207 for the initial alignment of the liquid crystal 110 injected between the color filter panel 200 and the TFT array panel 100 is provided.
The fabrication process of the color filter panel 200 of FIG. 2 will be explained in more detail with reference to FIGS. 3A to 3D.
Generally, a metal material or a resin for forming a black matrix is formed on a transparent substrate. The black matrix is formed between R, G, and B sub color filter layers and shields light passing through a reverse tilt domain formed at the periphery portion of a pixel electrode of a TFT array panel. As the material of the black matrix, a metal thin layer such as Cr having an optical density more than 3.5 or an organic material such as carbon are generally used. A double layer such as Cr/CrOx may be used for a low reflection. In case of using a metal thin layer, the black matrix may be formed in a certain pattern by a photolithography process applying an exposure process using a mask. On the other hand, in case of using a resin of an organic material, the black matrix may be formed in a certain pattern by an exposure process using a mask and a development process.
More specifically, FIG. 3A shows the black matrix 202 of a certain pattern formed on the substrate 201. In order to form the black matrix 202 on the substrate 201, a first mask including a black matrix pattern is needed and used.
After forming the black matrix 202, as shown in FIG. 3B, the color filter layer 203 composed of R, G, and B colors for displaying an image in colors is formed. The color filter layer 203 composed of R, G, and B sub color filter layers is formed such that each sub color filter layer corresponds to one of the unit pixels. The color filter layer 203 can be fabricated by using one of several methods such as a dyeing method, an electrodepositing method, a pigment dispersing method, a printing method, etc. Herein, the fabrication method of the color filter layer 203 by using the pigment dispersing method will be explained.
According to the pigment dispersing method, first, one of R, G, and B color resins is deposited on the substrate 201 where the black matrix 202 is formed. Here the color resins are deposited in the order of R, G, and B. Then, a selective exposure is performed on the resulting structure thereby to form a red sub color filter layer 203a. Then, a green color resin is deposited on the substrate 201 having the red sub color filter layer 203a, and a selective etching is performed thus to pattern and form a green sub color filter layer 203b at a corresponding region. Then a blue color resin is deposited and selectively etched to form a blue sub color filter layer 203c. 
In this regard, the sub color filter layers 203a, 203b, 203c are formed to have the same pattern. As a result, all the sub color filter layers 203a, 203b, 203c are formed by using one same mask having a certain pattern. This involves moving the same mask to a predetermined distance for each sub color filter layer and applying the mask process to form each of the sub color filter layers 203a, 203b, 203c. Consequently, to form the color filter layer 203, the mask process of exposure, development and cleaning has to be performed three times.
After forming the color filter layer 203 by performing the mask process three times, as shown in FIG. 3C, the transparent overcoat layer 204 of an organic layer for compensating the steps in the color filter layer 203 is formed.
After forming the overcoat layer 204, a transparent electrode as an indium tin oxide (ITO) layer for applying an electric field to the liquid crystal 110 is formed. This ITO layer serves as the common electrode 205.
Then, the spacer 206 for constantly maintaining a cell gap of the LCD device is formed on the common electrode 205. The spacer 206 is formed by using a dispersion method for dispersing spacer balls on the substrate or by using a patterning method which can be used to vary the size, height and position of the spacer.
The dispersion method is divided into a wet dispersion method for dispersing the spacer by mixing with alcohol, and a dry dispersion method for dispersing only the spacer. The dry dispersion method includes a static dispersion method using static electricity and an antistatic dispersion method using gas pressure. The antistatic dispersion method is mainly used in the liquid crystal cell structure susceptible to static electricity. By the dispersion method, the size, the height, and the position of the dispersed spacer balls cannot be easily varied. Accordingly, a patterned spacer (also called a column spacer) for increasing an opening ratio is used.
According to the patterning method for the spacer 206, a photosensitive resin is deposited on the common electrode 205 and an exposure process using a mask, a development process, and a cleaning process are performed thereto to form the spacer 206 of a certain pattern. Thus, to form the spacer 206, additional mask processes are required.
After forming the spacer 206 on the common electrode 205, an organic layer such as polyimide is deposited thereon for the initial alignment of the liquid crystal, and a rubbing is performed in a certain direction thus to form the alignment layer 207. This completes the fabrication of the color filter panel of the LCD device.
However, as aforementioned, since a large number of mask processes are required at the time of fabricating the related art color filter panel, the processes are delayed and the productivity of the LCD device is reduced. One mask process includes a series of processes such as a deposition process of a photosensitive resin, an exposure process, a cleaning process, etc. Therefore, it is advantageous to reduce the number of mask processes needed, so as to reduce the fabrication cost of the LCD device and to enhance the productivity of the LCD device.